1. Field of the Invention
The present invention relates to a single crystal growing apparatus and a single crystal growing method for manufacturing a dislocation-free single crystal of silicon by the pulling Czochralski method.
2. Description of the Prior Art
In a single crystal manufacturing apparatus based on the pulling Czochralski (CZ) method, fresh argon (Ar) gas is supplied into a highly pressure-proof airtight chamber made of graphite where pressure is reduced to about 10 torr in advance and polycrystal in a quartz crucible arranged in the lower portion of the chamber is melted by heating. Then, a seed crystal is immersed into surface of the melt from above, and by rotating and moving up and down the seed crystal and the quartz crucible, the seed crystal is pulled up. As a result, a single crystal (the so-called ingot) is grown, which comprises an upper cone portion with its upper end protruding, a cylindrical body portion, and a lower cone portion with its lower end protruding, all under the seed crystal.
As a method to grow as described above, Dash method is known. According to this method, in order to eliminate dislocation (i.e. in order to turn to dislocation-free), which occurs in the seed crystal due to thermal shock when the seed crystal is immersed to the surface of the melt, pulling rate is relatively increased after immersing the seed crystal to the surface of the melt so that a neck portion having smaller diameter than the seed crystal, e.g. 3 to 4 mm, is formed, and pulling of the upper cone portion is started.
Further, a single crystal having large diameter and heavy weight (150 to 200 kg or more) cannot be pulled up via the neck portion with small diameter, and a method has been proposed, for example, in JP-B-5-65477. According to this method, a neck portion with small diameter is formed by Dash method, and the pulling rate is then relatively slowed down and a portion with larger diameter is formed. Then, the pulling rate is relatively increased, and a portion with small diameter is formed. Thus, a "spherical constricted portion" is formed, and by gripping this constricted portion with a gripper, the single crystal having large diameter and heavy weight is pulled up. Also, a conventional type apparatus for gripping the constricted portion is proposed, for example, in JP-B-7-103000 and JP-B-7-515.
As other conventional examples, a method for directly gripping a body portion with a "constricted portion" as described above has been proposed, for example, in JP-A-5-270974 or JPA-7-172981. Also, a method to form a "ring-like constricted portion" having a larger diameter than the body portion between the upper cone portion and the body portion instead of the above "spherical constricted portion" and to grip this "ring-like constricted portion" has been proposed in JP-A-63-252991 and JP-A-5-270975.
However, in each of the conventional type gripping members as described above, there are problems in that it is not very practical to use a gripper and a power transmission mechanism to suspend a single crystal having large diameter and heavy weight (e.g. with a body portion of 400 mm in diameter and 400 kg in weight) in a chamber where pressure is reduced to about 10 torr using vacuum pump. If the single crystal is detached from the gripper and is dropped down, dislocation may occur, and the single crystal is not qualified as a product any more. When the quartz crucible is damaged, high temperature melt may react in the worst case with the cooling water inside the crucible shaft, which rotates and moves up and down the quartz crucible, and vapor explosion may occur.